The present invention relates to an NOx-cleaning paving structure, and more particularly to an NOx-cleaning paving structure in which a NOx-cleaning action and an excellent durability are provided to the surface layer of a paving layer or a surface layer constructed by Overlay method for a paving layer.
NOx is present in exhaust gas discharged from automobiles, particularly diesel motorcars. Air pollution caused by NOx has increased because of the increasing number of automobiles in use, because of increased traffic congestion, and the like.
Known NOx concentration-lowering materials include metal oxides, of which titanium oxide, more particularly titanium dioxide is known to have a strong photocatalytic action.
Research into removing NOx by the strong photocatalytic action has been more active nowadays. For example, the removal of NOx by using the external walls of buildings constructed of sheets or panels which incorporate titanium dioxide therein is nearing the commercial stage.
Under the above-mentioned situation, the present inventors have filed the patent applications of HEI 8-38137, HEI 8-58945, HEI 8-113507 and HEI 8-126659 relating to NOx-cleaning materials having titanium oxide in cement from the standpoint that a chemical stability is required for materials by which titanium oxide is held since titanium dioxide has a strong photoactivity.
The present inventors have now found that the following advantages can be obtained when NOx-cleaning materials are used as a surface layer provided to a road surface.
(1) The surface of road has many chances to be attacked by sunlight and rain as the surface thereof is flat with result that great effects are obtained for cleaning capability and refreshing.
(2) Paving layers can be simultaneously exchanged as a public office controls roads.
(3) As distances between roads and automobiles are short, an efficiency of contact with an exhausting gas including NOx is high.
Though there was proposed a plan of holding titanium oxide in asphalt in case of asphalt paving of paved roads, the asphalt used for general roads has a defect of deterioration cased by the photocatalytic action as well as a defect of a low NOx-cleaning capability.
In case of concrete paving, though can be made an NOx-cleaning structure having titanium oxide in the whole of the concrete, a large quantity of expensive titanium oxide is used, which is economically undesirable.
Considering the above-mentioned situation, in the former case of asphalt paving, the present inventors have found that a paved road without deterioration of asphalt and having an excellent durability can be obtained by providing an asphalt surface with a dough of cement and titanium oxide added thereinto, not by adding directly titanium oxide to asphalt to hold the titanium oxide in the asphalt and have found that by adopting porous asphalt, NOx-cleaning materials are penetrated into pores of porous asphalt with the result that an increased durability can be obtained.
In the latter case of concrete paving, the inventors have found that the expensive titanium oxide can be efficiently used either by providing a surface layer including titanium oxide on the concrete paving or by providing a surface layer including titanium oxide on a used concrete paving arranged by concrete overlay method.
The present invention has been carried out, based on the above-mentioned findings.
Accordingly, one object of the present invention is to provide an NOx-cleaning paving structure having a surface layer on a paving layer which is excellent in an NOx-cleaning action and durability.
Another object of the present invention is to provide an NOx-cleaning paving structure having a surface layer which is provided on a paving layer by overlay method and excellent in an NOx-cleaning action and durability.
The above-mentioned objects of the present invention are achieved by each of the following inventions (1) to (16).
Throughout the specification and the claims, the term xe2x80x9cfor paving purposesxe2x80x9d includes within its scope the xe2x80x9cpaving sideways or roadwaysxe2x80x9d. The NOx-cleaning paving structure of the present invention is provided with the following excellent effects.
(1) The basic NOx-cleaning paving structure of the present invention comprises a paving layer and a surface layer in order, the surface layer being obtained from 100 parts by weight of cement, 5-50 parts by weight of titanium oxide powder, 100-700 parts by weight of aggregate and 5-100 parts by weight of water. As the surface layer contains both cement and titanium oxide, the paving having an NOx-cleaning capability and an excellent durability is available.
(2) In the invention described in the above-mentioned (1), by adopting the paving layer composed of asphalt paving, the surface layer including titanium oxide is provided on the asphalt layer with the result that the asphalt layer is not deteriorated by titanium oxide, and as the surface layer contains cement, the surface layer is excellent in durability.
(3) In the invention described in the above-mentioned (1), titanium oxide can be contained only in the surface layer by adopting the paving layer composed of concrete paving, thereby to use expensive titanium oxide efficiently. Furthermore as the structure has the surface layer containing cement on the concrete paving, the concrete paving and the surface layer are strongly adhered each other, thereby to form paving having an enhanced durability.
(4) In the invention described in the above-mentioned (1), by adopting the paving layer composed of a part of used asphalt paving, there are available the effects of the present invention described in the above-mentioned (2) as well as it is not necessary to form again the paving from the beginning as the surface of the used asphalt paving is shaved off by overlay method and the surface including cement and titanium oxide is formed on the shaved part.
Accordingly excellent effects can be gained in the points that the term of work is shortened and the cost becomes small.
(5) In the invention described in the above-mentioned (1), by adopting the paving layer composed of a part of concrete paving, there are available the effects of the present invention described in the above-mentioned (3) as well as it is not necessary to form again the paving from the beginning as the surface of the used concrete paving is shaved off by well-known concrete overlay method and the surface layer including cement and titanium oxide is formed on the shaved part.
Accordingly excellent effects can be gained in the points that the term of work is shortened and the cost becomes small.
It goes without saying that the surface properties of the used paving layer can be recovered and the structure thereof can be strengthened.
(6) In the invention described in any of the above-mentioned (1) to (5), sunlight penetration is possible by limiting the thickness of the surface layer to from 1 to 300 mm and the catalytic reaction of titanium oxide can be performed efficiently.
(7) In the invention described in any of the above-mentioned (1) to (6), the work can be carried out efficiently by forming the surface layer using a dough including a high-performance reduction-water agent as the fluidity of the dough is improved in the work.
(8) In the invention described in any of the above-mentioned (1) to (7), the bending property and strength of the surface layer are afforded by forming the surface layer having 0.1 to 50 parts by weight of fiber, with the result that the enhanced durability of the paving is available.
(9) In the invention described in any of the above-mentioned (2), (4) or (6) to (8), a strong base layer for the asphalt layer is available by providing the asphalt layer with the base layer made of concrete, with the result that the paved road excellent in durability is available.
(10) In the invention described in any one of the above-mentioned (2), (4) or (6) to (8), a strong base layer for the asphalt layer is available by providing the asphalt layer with the base layer comprising a rock bed, with the result that the paved road excellent in durability is available.
(11) In the invention described in any of the above-mentioned (2), (4) or (6) to (8), the paving work cost is small and the work can be carried out efficiently by forming the base layer for asphalt comprising at least one selected from soil, macadam and stone, and the paved road formed has an NOx-cleaning capability corresponding to that of the paved road having the concrete base layer.
(12) In the invention described in any of the above-mentioned (2), (4) or (6) to (8), a part of the surface layer is penetrated into pores of a porous asphalt layer in the paving work by providing the asphalt layer which is porous, with the result that the surface layer and the asphalt layer are strongly adhered each other and the paving excellent in durability is available.
(13) In the invention described in any of the above-mentioned (1) to (12), the surface layer is strongly adhered by proving the surface of the paving layer with an unevenness with the result that the surface layer is excellent in durability, by which excellent effects are obtained for the paving of roadways.
(14) In the invention described in any one of the above-mentioned (1) to (13), the surface layer is enhanced in strength and a water seal thereof is increased by adding 10-50% by weight of an admixing additive comprising a pozzolan material relative to cement to form the surface layer with the result that the surface layer is enhanced in durability and in addition, there are available excellent effects such as strong resistance to an acid circumstance.
(15) In the invention described in any of the above-mentioned (1) to (13), a hydrant reaction is made dull by adding 10-50% by weight of an admixing additive comprising a blast furnace slag having a powder value less than 4000 m2/g relative to cement to form the surface layer.
(16) In the invention described in any of the above-mentioned (1) to (15), by adding 2-30% by weight of an adsorbing material relative to cement to form the surface layer, the following excellent effects are available: NOx is decomposed and removed by sunlight of days(ultraviolet rays included in sunlight) as well as NOx is adsorbed by the adsorbing material during nights and is decomposed by ultraviolet rays with the result of removing NOx.